Time delay for compressor motor circuit



Aug. 10, 1965 B. M. PAUL 3,199,306

TIME DELAY FOR COMPRESSOR MOTOR CIRCUIT Filed June 5, 1964 J17 T m I3 2o .8 \i I9 l6 A.C.SOURCE I {I LDS E f swn swz SW3 2:

1 14 5 HLFCs 36 (K l 29 PRSI P w I SR5 PR LLS q i m" 1 U 33 T5 SR TM PRS 2 BRUCE M. PAU L United States Patent fiice Patented Aug. 16, 1965 3,19%,3196 TIME DELA QQWZERESSGR Mfilifiii iIiRQUiT Bruce M. Paul, Eelieyiile, Nah, assignor to Worthington Corporation, Harrison, NJ a corporation of Delaware Fried dune 5, 1964, Sea. No. 3729329 3 Saints. (Ci. 62-453) This invention relates to a motor control circuit, it relates in particular to a circuit for controlling operation of a motor compressor in a refrigeration system adapted to avoid unnecessary recycling of the compressor.

Recycling or a short cycling as used in the following description refers to a condition wherein the compressor motor, normally connected to a source of electrical current, is caused to restart frequently soon after stopping. Such repeated start-ups may be attributed to several effects. Primarily, the compressor motor is normally actuated in response to the load on the refrigeration system. For convenience, such control is associated with fluid flow from the system evaporator, as well as refrigerant flow in the system.

One condition found to cause recycling regardless of the loading condition on the system, occurs when excessive leakage of refrigerant gas to the system compressor pr0- Vides a false load indication due to the buildup of gaseous refrigerant in the compressor. If such refrigerant leakage is excessive, the compressor will repeatedly recycle to pump down, and thereby cause undue Wear and possible physical damage to the motor and its starting components.

Where the refrigeration system control includes other equipment such as pumps, fans, valves, etc, it is readily apparent that not only will the compressor be adversely effected by recycling, but the whole system is jeopardized.

To overcome excessive and repeated compressor recycling, the present invention provides time delay means in the control circuit for the system. Said control circuit embodies a timer device preset, and connected to the compressor current supply lines. Said control circuit includes a plurality of switches connected in parallel, and interposed in series with the compressor current supply, each of which switch is operated independently to complete the compressor motor circuit.

The invention relates particularly to a refrigeration system in which the motor is a component thereof to drive a hermetic compressor. Said motor is connected to the power source through the time delay device which is operable after each stoppage of the drive motor to prevent restarting within a predetermined time period. Also included in the circuit is means to lay-pass the timer arrangement to permit a startiru up of the refrigeration system when the need for cooling arises, regardless of the timing delay arrangement.

it is therefore an object of the invention to provide an improved compressor control circuit embodying means for preventing shortcycling of the compressor motor.

A further object of the invention is to provide an elec trical circuit connected to a compressor motor and in cluding time delay means interposed in the circuit for avoiding rapid recycling of the motor due to accumulation of refrigerant in the compressor.

Still another object of the invention is to provide in a refrigeration system having a motor driven compressor, a means for protecting said motor by avoiding rapid recycling caused by migrating refrigerant passing into the compressor during periods when the compressor is out of operation.

These and other obg'ects of the invention will become clear to those skilled in the art from the following description made in coniunction with the accompanying drawing.

The single figure is a schematic drawing of the present control system shown embodied in a schematically illustrated refrigeration system.

Referring to the drawing, an embodiment of the control circuit is shown incorporated into a closed refrigeration system comprising well known refrigeration components. Compressor it may be of the centrifugal or the recipro eating type and includes a shaft extending therefrom and coupled to a drive motor 11. The latter is electrically connected to a source of current indicated as lines Lll and L2.

Compressor it is communicated through line 12 to the inlet side of condenser 13, directing a stream of hot refrigerant gas to the latter. Condenser 13 may be exposed to the atmosphere, or provided with a fan 14 for passing ambient air or other heat transfer medium across refrigerant carrying coils. In the condenser, refrigerant is trans formed to liquid phase and carried as liquid through conduits l7, receiver 15, and expansion means 16 to the inlet of evaporator 18.

In the expansion means 16, normally an expansion valve, expanded refrigerant is metered into heat exchange coils of evaporator 18, which are in heat exchange contact with a medium to be cooled. After being vaporized in evaporator 313, the gaseous refrigerant is passed in suction line 19 and thence redirected to the suction inlet of compressor 1%.

The compressor motor in the system may be of the open or the hermetic type that is, enclosed completely in a single casing, without altering the function of the presout control means. Referring to the electrical schematic section of the figure, the compressor motor is provided with a two line source of alternating current, L1, L2.

line disconnect switch LDS is included in a manually operated starter having fuses Flt and F2 connected to protect the motor circuit from overloading.

Following standard practice, a motor switch MS which is represented in the circuit by an energizing coil, is protected from overheating by one or more current interrupting devices represented as switches SW1, SW2. and SW3, which are connected into the supply lines L1 or L2 and are exposed to the motor temperature. These switches may be actuated by a thermal element imbedded in the motor windings, or by a thermally resistive member positioned in the motor casing or as a part of overload relays, which might be incorporated into the system. Said switches control the current supply to the motor and function to hold the motor circuit open so long as motor overheating persists. ln hermetic units of the type contemplated, cooling of internal components is usually achieved by passing low pressure refrigerant gas from the evaporator to the motor casing, prior to the introduction of said gas to the compressor. Thus the degree of cooling achieved at the motor is critical, consequently the use of suitable thermal protection is desirable.

Motor switch MS is connected electrically to current supply l ne L2, and through wire 23 to switch HLPCS which is responsive to a high-low pressure cutout relay actuated in accordance with the circuit refrigerant pressure. As shown in the figure, the HLPCS switch responds to pressure at condenser 13 upstream side, and at the evaporator downstream side, such that the pressure parameters of the refrigeration system might be maintained between predetermined values.

Pressure switch PS is connected through line 24 to series connected switches SW3, SW21, andSW3, thence to line Li. Pressure switch P8 is actuated to open and closed position through sensing means responsive to the compressor pressure, and is the element that normally senses the presence of excessive refrigerant build-up downstream of the evaporator or in the low pressure suction side of compressor Ill.

Protective relay coil 26 is connected to line L2,, and in parallel to switches MS and HLPCS. Protective relay coil PR includes an energizing coil activating two contacts PRSli and PRSZ. One side of coil 26 is connected through the normally open contact 'PRST to a'terminal and SRS, each of which contacts is operable to connect motorswitch MS to the current source as will be hereinafter explained.

A sustaining relay SR'includes anenergizing coil 2'7 connected through lines 28 to line L2. Coil LLS is connected to line L2 in parallel with energizing coil 27. Coil LLS functions to control the flow of refrigerant through valve 2%) to initiate fluid flow through the refrigeration system as the compressor approaches operating conditions. A temperature responsive switch TS is connected in series with sustaining relay SR and with coil LLS. Actuating means associated with switch TS is in intimate contact'with refrigerant leaving evaporator 18 to in eifect sense the load imposed on'the system. As the temperature in refrigeration line 19 decreases, indicating a decrease in load on the system, switch TS will open thereby de-energizingcoil 27, and coil LLS.

The circuit timer device includes a timer motor TM operably connected through a suitable step-down gear train to a rotatable arm driven at a fraction of theshaft speed of TM. The slowly rotating arm is set to contact a normally open switch TDS, closing the circuit through motor switch MS.

It is understood that the timer motor TM presently shown, may assume a number of embodiments familiar to the art, and may be adapted to function within the circuit as will be hereinafter described.

Normally, and as presently shown, after the timer device has transversed a predetermined time cycle, the timer is automatically reset to a starting position in preparation for commencing another time cycle.

Suitable adjusting means may be built into the timer to permit delay of the compressor motor startup for any suitable time depending on the characteristics of the motorand the refrigeration circuit.

Operation 7 In the operation of the refrigeration system, startup of the compressor motor is initiated by closing switches LDS in the main disconnect switch. This disconnect as shown, includes a double pole single throw switch. It is appreciated however, that the disconnect may include the usual magnetic or electrically actuated relay having contactsof suiiiciently large capacity to take the high starting current drawn from lines L1 and L2 by the motor switch MS.

It is assumed for the purpose of the present description that safety switches SW1 through SW3: respectively are closed, a condition indicating no damage or discontinuity in the windings of the motor field, starting and stator coils. .If the temperature in the refrigeration system indicates a demand for cooling, temperature switch TS is closed. Thus, as current is supplied through lines L1- L2, temperature switch TS closes a circuit through line 33, switch TS and line 34. Current through energizing coil 27 closes contacts SRS. Energization of coil LLS adjusts valve Ztl thereby permitting how of liquid refrigerant from receiver 15 to expansion valve 16 and evaporator 18. a

If the switch HLPCS is closed, energization of coil 27, closes contacts SRS thereby completing the circuit from line L1 through switches SW1, SW2 and SW3 inclusive, switch PS, contacts SRS, switch HLPCS, and motor switch MS to line L2. Closing of contacts SRS also completes a circuit through coil 26 which in turn opens contacts PRSZ and closes contacts PRSl.

With contacts PRSZ, open, the timer motor TM is locked out of the circuit. Thus under normal running conditions, contacts PRSl, SRS are closed and contacts TDS is open.

As cooling load imposed on the refrigeration system is satisfied, and the temperature of the evaporator decreases, switch TS opens, thereby interrupting current flow through coil 27 of sustaining relay SR, and through coil LLS thereby itnerrupting flow of refrigerant to evaporator ilii. Reduced refrigerant pressure at evaporator 18 causes switch PS to open thereby interrupting current flow to coil MS, and consequently stopping the com- 'pressor.

As coil 26 becomes tie-energized, contacts PRSZ aslsume a normally closed position and apply current across the energizing windings of tirner motor TM causing contacts TDS to revert to the normally open position. Thus contacts TDS, PRST and SRS are all open and TM has commenceda preset timed cycle.

If compressor crank case members, such as valves and glands, etc.,. develop a defect, there will be a consistent leakage of refrigerant into the crankcase or the low pressure chamber of the compressor thereby building up the pressure therein. Without the present control arrangement, such pressure build-up in the compressor will close switch. PS thereby initiating operation of motor switches MS, to put the compressor into a pump down cycle; However, according to the objectives of the present invention, regardless of the pressure indication at switch PS even though the latter closes, contacts TDS, PRSl and SRS maintain the motor switch MS open.

During the timed delay cycle, after a compressor motor stoppage when timer motor TM is energized, motor switch MS will be able to dissipate any heat accumulated during the operating periodj Thereafter, at the lapse of the timed delay, switch PS may be closed due to increase in refrigerant pressure and at the end of the timed cycle, the actuating members of TM, functions to momentarily close contactsTDS, thereby momentarily completing the circuit through switch PS, contacts TDS, switch HLPCS, tomotor switch MS. V

, Assuming, switch PS to be closed, simultaneously, contacts TDS complete the circuit through switch PS, contacts TDS, line 36, coil 26, and line 29, to power line L2 to energize the coil. As the latter is energized contacts PRST are closed, and contacts PRSZ open in that sequence,

Closing of contacts PRST holds the motor switch MS closed even though contacts TDS remains open. Opening of contacts PRS2 interrupts the current flow to timer motor TM, which in turn opens contacts TDS after the momentary closing of the latter to initiate current flow into compressor motor 131.

Contacts PRSll and PRSZ actuate in a make-beforebreak sequence to achieve two purposes. First, making of contacts PRSil, assures that the motor switch MS is energized through L1 and L2, to start up the compressor. Secondly, protecting relay PR coil 26 becomes energized to open contacts .PRSZ thereby avoiding recycling of the timer motor TM through its complete delay period.

f Motor switch MS will now continue to function for compressing refrigerant, and passage thereof through the refrigeration circuit until such time as'the evaporator pressure is sufficiently reduced to open switch PS.

The present arrangement as mentioned, avoids rapid recycling of the compressor motor in response to a buildup in the compressor due to refrigerant leakage in the compressor. It further permits the time delay period to be by-passed or to be shortened in the event the conditions at the system evaporator dictate a need for further cooling or starting up of the refrigeration system.

For example, during the delay cycle regarless of the position of switch PS, contacts TDS, PRSI and SRS are opened, switch HLPCS is closed, contacts PRSZr are closed, and timer motor TM is energized.

A sudden demand for cooling will be signified by a closing of switch TS to complete the circuit through line 33, switch TS, line 34, coil 27 of the sustaining relay SR, and line 28 to line L2.

Energizing of coil 27 closes contacts SRS to complete the circuit through switch PS, and contacts SRS, line 36, coil 26 of protecting relay PR and coil 27. Energizing coil 27 further opens contacts PRSZ and interrupts the current flow to timer motor TM regardless of the time elapsed since the commencing of said timer cycle.

Thus, the disclosed control arrangement permits safe operation of a refrigeration system in such manner as to permit periodic pump down of the compressor to evacuate migrating refrigerant therefrom. It further protects the compressor motor system by avoiding the rapid recycling. The third feature incorporated into the instant arrangement is the characteristic of the circuit whereby the time delay period might be by-passed or interrupted to institute operation of the compressor to meet a load being imposed on the system at any time during the time delayed cycle.

It is understood that the present circuit represents a preferred embodiment of the invention and that certain modifications and changes may be made therein without departing from the spirit and scope of the invention.

' What is claimed is:

1. A control circuit for refrigerant compressor motor forming a portion of closed system circulating a refrigerant, Which system includes the compressor, a condenser, and an evaporator, said control circuit comprising:

(a) compressor motor switching means for connecting and disconnecting said compressor motor to and from a source of electrical power,

(b) temperature sensing means operative to measure the temperature of refrigerant and to energize said compressor motor switching means when the refrigerant temperature rises above a predetermined value to cause said compressor motor to be connected to the source of electrical power, said temperature sensing means being further operative to cause said compressor motor switching means to disconnect said compressor motor from the source of electrical power when the temperature of the refrigerant drops below a predetermined value,

(c) pressure sensing means operative to cause said compressor motor switching means to disconnect the compressor motor from the source of electrical power when the refrigerant pressure falls outside of a predetermined pressure range,

(d) time delay means operative through said compressor motor switching means when said compressor motor is disconnected from the source of electrical power to initiate a time delay switching operation during which time delay period the compressor motor is maintained disconnected from the source of electrical power except for (e) said temperature sensing means being operative to connect the compressor motor to the source of electrical power whenever the temperature of the refrigerant in the system rises above the predetermined value.

Z. The control circuit of claim including (a) refrigerant flow control means, said refrigerant flow control means being operative to cutoff the flow of refrigerant in the system.

(b) said tempearture sensing means being further operative to cause said refrigerant flow control means to cutolf refrigerant flow in the system when the temperature in the system drops below the predetermined value.

3. The control circuit of claim 1 including:

(a) compressor motor temperature sensing means operative to cause said compressor motor switching means to disconnect the compressor motor from the source of electrical power when the temperature of the compressor motor exceeds a predetermined value.

References Cited by the Examiner UNITED STATES PATENTS 2,556,882 6/51 Minkler et a1 62-226 X 2,720,084 10/55 Hailey 62226 3,037,364 6/62 Tucker et al. 62158 3,135,908 6/64 Harris 62-158 X ROBERT A. OLEARY, Primary Examiner.

LLOYD L. KING, Examiner, 

1. A CONTROL CIRCUIT FOR REFRIGERANT COMPRESSOR MOTOR FORMING A PORTION OF CLOSED SYSTEM CIRCULATING A REFRIGERANT, WHICH SYSTEM INCLUDES THE COMPRESSOR, A CONDENSER, AND AN EVAPORATOR, SAID CONTROL CIRCUIT COMPRISING: (A) COMPRESSOR MOTOR SWITCHING MEANS FOR CONNECTING AND DISCONNECTING SAID COMPRESSOR MOTOR TO AND FROM A SOURCE OF ELECTRICAL POWER, (B) TEMPERATURE SENSING MEANS OPERATIVE TO MEASURE THE TEMPERATURE OF REFRIGERANT AND TO ENERGIZE SAID COMPRESSOR MOTOR SWITCHING MEANS WHEN THE REFRIGERANT TEMPERATURE RISES ABOVE A PREDETERMINED VALUE TO CAUSE SAID COMPRESSOR MOTOR TO BE CONNECTED TO THE SOURCE OF ELECTRICAL POWER, SAID TEMPERATURE SENSING MEANS BEING FURTHER OPERATIVE TO CAUSE SAID COMPRESSOR MOTOR SWITCHING MEANS TO DISCONNECT SAID COMPRESSOR MOTOR FROM THE SOURCE OF ELECTRICAL POWER WHEN THE TEMPERATURE OF THE REFRIGERANT DROPS BELOW A PREDETERMINED VALUE, (C) PRESSURE SENSING MEANS OPERATIVE TO CAUSE SAID COMPRESSOR MOTOR SWITCHING MEANS T DISCONNECT THE COMPRESSOR MOTOR FROM THE SOURCE OF ELECTRICAL POWER WHEN THE REFRIGERANT PRESSURE FALLS OUTSIDE OF A PREDETERMINED PRESSURE RANGE, 